Verses 2-6 of Chapter 4:

Restore to the orphans their property, and do not exchange your worthless things for their valuable things, and do not devour their property by mixing it up with your own, for it is a great sin. And if you be apprehensive that you will not be able to do justice to the orphans, you may marry two or three or four women whom you choose. But if you apprehend that you might not be able to do justice to them, then many only one wife, or marry those women who have fallen in your possession. This will be the better course to avoid injustice. And give their dowries willingly to women (as an obligation), but if they, of their own accord ,remit a portion of the dowry, you may enjoy it with pleasure. Do not give to the feeble-minded people that property which Allah has made the means of your maintenance: you should however, provide them with food and clothing and give them good advice. And go on observing and testing the orphans until they reach the marriageable age:  then if you perceive that they have become capable, deliver to them their property. Be on your guard against devouring their property unjustly and wastefully and hastily lest they should grow up to demand it. If the guardian of an orphan is rich, let him abstain from the orphan's property, and if poor, let him eat of it fairly.When you hand over to them their property, then have some people to witness it, and Allah suffices as Reckoner.